In a brush-type motor, alternate magnetic attraction and repulsion between poles in the armature and stator cause the armature to rotate when a current flows through the stator and armature windings. The current flow through the armature windings must continually be reversed to provide such an alternate action. A commutator and brushes are used to continually and alternately switch the current in the armature windings as the armature rotates. A conventional commutator includes commutator segments, separated by slots, disposed around an insulating core press-fit onto the armature shaft, with wire tangs or hooks connecting each segment to the armature windings.
Armature reaction varies according to the geometry and symmetry of the armature windings and the commutator segment position. For efficient motor operation the commutator must be precisely circumferentially positioned on the armature shaft with respect to the armature core position to minimize any effects of armature reactions. In an attempt to properly align commutators on armature shafts, manufacturers have aligned commutators according to the positions of the tangs with respect to a known position for the armature poles or slots. One of the problems with this procedure is that the tang position with respect to its associated comutator segment depends on the accuracy of the metal forming operation and metal stamping operation utilized in constructing the commutator. As described in Wojcik co-pending U.S. patent application Ser. No. 855,393, the slots which define the segments are typically cut into the commutator as one of the last steps in the commutator assembly. Thus, the inaccuracies resulting from the metal forming operation, the stamping operation, and slot positioning operation accumulate which may result in inaccurate positioning of the tangs with respect to each commutator segment.
An alternative approach to aligning the commutator relies on the circumferential alignment of a single commutator slot with respect to a known armature position. It is believed that such an alignment procedure results in a more accurate positioning of the commutator, to provide more precise switching of armature current, resulting in more efficient motor operation than obtained by keying upon tangs for alignment.
One known method for aligning the commutator according to slot position utilizes an optical sensor to accurately position a single commutator slot relative to a known armature core position. This procedure requires an accurate light source, such as a laser, which is expensive. Moreover, this method assures only that a single commutator slot will be aligned properly. If the circumferential spacing between slots is not identical, then improper alignment may result, again rendering the motor less efficient than it could be should each bar be properly aligned with the armature winding.
The above described problems while important in a two pole motor, are even more critical in a motor having a greater number of poles. With a four pole motor, the armature current, and thus armature voltage, goes through two complete cycles each revolution. Therefore, to balance armature reactions between sets of poles there must be a more precise orientation than with a two pole motor.
The present invention is directed to overcoming these and other problems relating to motor armature construction.